1. Field of the Invention
The present invention generally relates to a computer apparatus, and, more particularly, to the electromagnetic interference (EMI) shielding of personal computers.
2. Description of the Related Art
Radiation sources for electromagnetic waves have been increasing in number with continued advances in industrial technology. The leakage of electromagnetic waves, therefore, has become a significant problem since the wave can exert adverse influences on the human body and cause incorrect behavior of integrated circuits in electronic equipment, particularly electronic computers.
With the constant technological advances in the computer industry, such as faster, higher resolution displays, faster memory, faster processors, etc., comes the problem of EMI containment and shielding. Personal computer systems have attained widespread use in the world. These personal computing systems now provide computing power to many segments of today's modern society. A personal computer system can usually be defined as a desktop, floor-standing, or portable microcomputer that includes a system unit having a system processor with associated volatile and non-volatile memory, a display monitor, a keyboard, one or more floppy diskette drives, a hard disk storage device and an optional printer. One of the distinguishing characteristics of these systems is the use of a system board or mother board, which includes a ground plane, and which electrically connects these components together. In general, since metals can absorb or reflect electromagnetic waves, they are effectively used as shielding materials. In addition, plastics with metals deposited thereon, or plating, can be used for the same purpose, for example, metal plating of either the plastics in portable computers or the chassis in desktop computers.
Plating is used in portable and desktop computers to provide a Faraday Cage (an arrangement of a conducting sheet or conducting mesh bonded together so that an EMI shield is provided, but connected in such a way that induced currents cannot circulate) to contain EMI. The plating contains the EMI and, through a ground path connection, directs it to the ground plane. For the plating to be most effective, the ground path connection should have the least impedance possible. Mechanical methods, such as wires screwed to the plating, copper or metal grounding straps contacting the plating and ground are used to make the connection to ground. Other methods involve plating touching plating or some other metal component connected to the ground plane. These methods create a high impedance connection, thus limiting the effectiveness of the plating. Accordingly, a design and method is needed which creates a low impedance connection between the plating and the ground plane.